Summary

We applied nonparametric statistical techniques to historical streamflow data from five glacierized and four nonglacierized watersheds in southwest Yukon and northwestern British Columbia, Canada, to determine whether rivers with and without catchment glacial cover respond in significantly different ways to a warming climate. The analysis was posed in terms of contrasts between the two groups with respect to long-term trends in annual time series of total river flow volume. We found that glacier-fed rivers grew larger and nival streams progressively smaller over the historical record under an observed regional warming trend. Although some of these trend effects are subtle, the overall result was statistically significant at restrictive [...]

Summary

We applied nonparametric statistical techniques to historical streamflow data from five glacierized and four nonglacierized watersheds in southwest Yukon and northwestern British Columbia, Canada, to determine whether rivers with and without catchment glacial cover respond in significantly different ways to a warming climate. The analysis was posed in terms of contrasts between the two groups with respect to long-term trends in annual time series of total river flow volume. We found that glacier-fed rivers grew larger and nival streams progressively smaller over the historical record under an observed regional warming trend. Although some of these trend effects are subtle, the overall result was statistically significant at restrictive confidence levels. Combined consideration of hydrological, meteorological and glaciological trends suggests that the streamflow consequences of increasing temperature exceed those from a concurrent rise in precipitation in the study area, causing increases in both glacial meltwater production and evapotranspiration; the former appears to have the dominant net hydrologic effect in glacierized catchments, and the latter in glacier-free watersheds. By empirically demonstrating that catchment glacial cover can result in opposite trends in total annual flow volume from river to river within an otherwise hydroclimatologically uniform area, the analysis presents strong evidence that climatic warming can materially affect downstream water resources specifically via glaciological pathways, and also implies that regional generalizations of interpreted or projected hydrologic trends may not be tenable in variably-glacierized regions.